Method of controlling combustion

Abstract

A method of controlling combustion in a furnace of a boiler or the like having a burner for a main combustion and a burner for a reducing combustion in order to effect combustion for furnace denitrification. The method comprises the steps of: estimating the NO x generation amount from data on a flame formed by the main combustion; estimating the reducing agent generation amount from data on a flame formed by the reducing combustion; and controlling the flow rates of fuel and air supplied for the main and reducing combustions so that the amount of NO x emission as the difference between the NO x generation amount and the reducing agent generation amount is below a specified value. In practice, each of the NO x generation amount and the reducing agent generation amount is estimated from the flame pattern, the flame volume, the distance between the outlet of the burner concerned and the root of the flame concerned, etc., thereby to distributively control the flow rates of fuel and air supplied to each of the main combustion burner and the reducing combustion burner so that the amount of NO x emission is below a specified value.

What is claimed is: 
     
       1. A method of controlling combustion in a furnace in which a main combustion takes place followed by a reducing combustion and which has a burner for the reducing combination disposed in the stage subsequent to a burner for the main combustion in order to effect combustion for such a furnace denitrification that nitrogen oxides (NO x ) generated in the main combustion zone by said main combustion burner are reduced by a reducing agent generated in the reducing combustion zone by said reducing combustion burner, said method comprising the steps of: observing combustion flames formed by said main combustion burner and by said reducing combustion burner with image guide means operatively associated with said burners;   estimating the reducing agent generation amount on the basis of at least data on a pattern of a combustion flame formed by said reducing combustion burner among the data obtained from the observation of the combustion flame formed by said reducing combustion burner;   estimating the NO x  generation amount on the basis of at least data on a pattern of a combustion flame formed by said main combustion burner among the data obtained from the observation of the combustion flame formed by said main combustion burner; and   controlling the amount of fuel supplied to at least one of said main combustion burner and said reducing combustion burner so that said estimated reducing agent generation amount and NO x  generation amount will be coincident with respective predetermined target values thereof to thereby control the amount of NO x  emission from said furnace below a predetermined value.   
     
     
       2. A method of controlling combustion according to claim 1, wherein an estimated value of the volume of said flame is employed as said data on the flame pattern. 
     
     
       3. A method of controlling combustion according to claim 2, wherein said flame volume is operationally estimated as the product of the length of said flame and the flame width squared. 
     
     
       4. A method of controlling combustion according to claim 2, wherein said flame volume is operationally estimated from the projected area of said flame. 
     
     
       5. A method of controlling combustion according to claim 4, wherein said flame projected area is operationally estimated as the product of the length and width of said flame. 
     
     
       6. A method of controlling combustion according to claim 2, wherein a new flame volume in the case where there are variations in amount of fuel supplied is operationally estimated as a value proportional to the 3/2 power of the change ratio of the projected area of said flame. 
     
     
       7. A method of controlling combustion according to claim 6, wherein said new flame volume is operationally estimated as a value proportional to the cube of the change ratio of the projected width of said flame. 
     
     
       8. A method of controlling combustion according to claim 1, wherein the NO x  generation amount is operationally estimated on the basis of the distance (d M ) between the outlet of said main combustion burner and the root of the flame formed by said main combustion. 
     
     
       9. A method of controlling combustion according to claim 1, wherein the NO x  generation amount (F gNOx ) is estimated from the volume (V M ) of the flame formed by said main combustion, the distance (d M ) between the outlet of said main combustion burner and the root of the flame formed by said main combustion, the temperature (T g ) of the combustion gas in said main combustion zone, and the nitrogen partial pressure [P N  ] in said main combustion zone, through the following equation: ##EQU26## where, kg: a rate constant of generation of NO x   A M  : a constant.   
     
     
       10. A method of controlling combustion according to claim 1, wherein said reducing agent generation amount is operationally estimated on the basis of the distance (d R ) between the outlet of sad reducing combustion burner and the root of the flame formed by said reducing combustion. 
     
     
       11. A method of controlling combustion according to claim 1, wherein said reducing agent generation amount (F rNOx ) is estimated on the basis of the volume (V R ) of the flame formed by said reducing combustion, the distance (d R ) between the outlet of said reducing combustion burner and the root of the flame formed by said reducing combustion, the temperature (T R ) of the reducing combustion gas, and the NO x  partial pressure [P NOx  ] in said reducing combustion zone, through the following equation: ##EQU27## where, k r  : a rate constant of reduction A R  : a constant.   
     
     
       12. A method of controlling combustion according to claim 11, wherein said reducing agent generation amount (F rNOx ) is operationally estimated as a value proportional to said NO x  generation amount (F gNOx ). 
     
     
       13. A method of controlling combustion according to claim 1, wherein said flame pattern is obtained as a region in a measured flame picture image which has a luminance or temperature above a predetermined level. 
     
     
       14. A method of controlling combustion according to claim 1, wherein the flow rate of pulverized coal as the flow rate of fuel supplied to each of said burners is estimated by the use of the Kalman filtering. 
     
     
       15. A method of controlling combustion according to claim 1, wherein said image guide means include optical fiber means positioned closely adjacent to the combustion flames formed by said main combustion burner and said reducing combustion burner and said method further comprising guiding combustion flame data outside of each of said combustion zones with said optical fiber means to an image pickup camera.